<!DOCTYPE HTML>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>alert</title>
    <script type="text/javascript">
        function rec(){
            var mychar="I love JavaScript";
            alert(mychar);
        }
    </script>
</head>
<body>
<input name="button" type="button" onClick="rec()" value="点击我，弹出对话框" />
</body>
</html>